"Yeah, it was," Steve nods. "Like I said, I know it sounds weird but Hawkins isn't exactly what you'd call a normal town. Back when Will Byers and Barbara Holland went missing? That was all related to the clock guy, too. It's a whole... situation."

Calling the Upside Down and everything that goes with it a situation is a bit of an understatement but he's going to ease into that. No need to plunge Chrissy right into the pool of crazy. She can dip her toes, first. They'll work up to "there's an alternate dimension that's just like a scary copy of Hawkins and full of monsters and also remember when Billy Hargrove died in that mall fire? Yeah, that was monsters, too" in due time.

He'll just leave it at that for now, in case she has any questions. Or, like, totally understandable doubts.